1. Field of the Invention
The present invention relates to a conductive oxide film, a display device, and a method for forming a conductive oxide film.
The present invention relates to a conductive oxide film having a crystal structure in which c-axes are aligned in a direction perpendicular to a surface of the film, and a method for forming the conductive oxide film. In addition, the present invention relates to a display device using such a conductive oxide film.
2. Description of the Related Art
Recently, touch panels having a multi-touch function have widespread rapidly in accordance with the increasing demand for smartphones or tablet PCs. Transparent conductive oxide films are utilized in touch panels, thin-film solar cells, and particle moving type electronic paper using electronic liquid powder. The demand for high-quality transparent conductive oxide films is expected to increase, and the market of the films will expand in the future.
Materials that are used for the transparent conductive oxide films are roughly classified into crystalline materials and amorphous materials. Examples of the crystalline materials are indium tin oxide (ITO) and zinc oxide (ZnO), and an example of the amorphous materials is indium zinc oxide.
ITO is the most general material of the transparent conductive oxide film, and a sputtering method is the most general method for forming the transparent conductive oxide film. For the transparent conductive oxide films, a reduction in cost of the film formation and the material as well as several properties such as high transmittance of visible light, high conductivity, and low electric resistance is required.
As a factor for indicating the conductivity of the transparent conductive oxide films, sheet resistance is used. For the uses of electronic paper, a sheet resistance of approximately 300Ω/□ to 400Ω/□ is enough for operation; however, a sheet resistance of 200Ω/□ or lower is desired for the uses of touch panels.
The sheet resistance depends on carrier density and mobility. As the sheet resistance becomes lower, the carrier density becomes higher or the mobility becomes higher, which means higher conductivity. Further, the sheet resistance depends on thickness. For example, the sheet resistance of an ITO film with a thickness of 30 nm is approximately 100Ω/□, and that with a thickness of 200 nm is approximately 10Ω/□.
In Patent Document 1, a method for forming a dense ZnO film having crystallinity is disclosed.